Modern telecommunication systems include heterogeneous mixtures of second, third, and fourth generation (2G, 3G, and 4G) cellular-wireless access technologies, which may be cross-compatible and may operate collectively to provide data communication services. Global Systems for Mobile (GSM) is an example of 2G telecommunications technologies; Universal Mobile Telecommunications System (UMTS) is an example of 3G telecommunications technologies; and Long Term Evolution (LTE), including LTE Advanced, and Evolved High-Speed Packet Access (HSPA+) are examples of 4G telecommunications technologies.
In most cases, wireless devices may initiate an emergency call on any wireless network using any access technology, regardless of whether the wireless device is a subscriber to particular wireless network or telecommunication system. However, network factors such as quality, reliability, and location accuracy vary amongst networks. In an emergency situation, network connectivity can be critical.